R help - Nov 2010 - How to pick out several infinite values when calculating means?

Dear r-help,

I want to use tapply to calculate means for a variable. But there were several
infinite values in the observations.

How can I calculate means not considering  these infinite values?

Thanks in advance.


Regards,
Lei


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Hi Lei,

Here is one option relying on is.finite()


## Messy data for means
dat <- data.frame(values = c(rnorm(7), 1:7, c(1, 2, 3, NA, 4, 5, 6),
  c(1, 2, Inf, 4, 100, -Inf, NaN)), group = rep(letters[1:4], 7))

## use is.finite() to select for only finite numbers
tapply(dat$values, dat$group, function(x) {mean(x[is.finite(x)])})

if you wanted to just exclude infinite values, but keep NAs (I don't
know why you would but...), you could use !is.infinite() to get values
that are not infinite.

Cheers,

Josh

On Tue, Nov 16, 2010 at 1:24 PM, Lei  Zhou <Lei.Zhou at agrsci.dk>
wrote:
> Dear r-help,
>
> I want to use tapply to calculate means for a variable. But there were
several infinite values in the observations.
>
> How can I calculate means not considering ?these infinite values?
>
> Thanks in advance.
>
>
> Regards,
> Lei
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/